Film-spreader

ABSTRACT

Apparatus and method for maintaining uniform tension in a travelling web by feeding the web around a hinged spreading member disposed transversely of the web, resiliently biassing at least a terminal portion of the spreading member into cooperating engagement with at least a marginal portion of the web and withdrawing the web against the biassing influence of the terminal portion.

United States Patent 1 Hasler 1 1 Sept. 23, 1975 FILM-SPREADER [76] Inventor: Robin Hasler, 52 Camper Crescent,

Bengeo, Hertford, Hertfordshire, England [22] Filed: July 24, 1972 [21] Appl. No.: 274,429

[30} Foreign Application Priority Data Aug 3, 1971 United Kingdom 36.416/71 [52] US. Cl 226/7; 226/97; 226/192; 226/195; 226/198 [51] Int. Cl B65h 25/02 [58] Field of Search 226/7. 1, 195. 198, 197, 226/192, 97; 26/6167: 270/5215 [56] References Cited UNITED STATES PATENTS |,927,s49 9/1933 Roberts 1. 226/192 x Robertson 4, 26/63 Derrick 226/l95 UX Primary E.raminerRichard A. Schachcr Attorney, Agent, or Firm-Cushman, Darby & Cushman [57] ABSTRACT Apparatus and method for maintaining uniform ten sion in a travelling web by feeding the web around a hinged spreading member disposed transversely of the web, resiliently biassing at least a terminal portion of the spreading member into cooperating engagement with at least a marginal portion of the web and withdrawing the web against the biassing influence of the terminal portion.

13 Claims, 5 Drawing Figures US Patent Sept. 23,1975 Sheet 2 of2 3,907,186

FILM-SPREADER This invention relates to a travelling web of material, such as a thermoplastic film, and in particular to a method and apparatus for equalising the tension in such a travelling web.

In the course of producing or treating a continuous web or film it is usually necessary to convey the web to several locations or treatment stations in turn, and this is usually accomplished by means of a system of rollers over or around which the web is threaded before being wound up onto a storage reel. To reduce the incidence of wrinkles in the web both during transportation of the web, and in the finally reeled-up web, it is desirable to equalise, as far as possible, the longitudinal tension imposed on elements of the web located across the width of the web.

According to the present invention we provide a method of maintaining substantially uniform longitudinal tension in a travelling web which comprises feeding the web around a hinged spreading member disposed transversely of the web, resiliently biassing at least a terminal portion ofthe spreading member into cooperating engagement with at least a marginal zone of the web as hereinafter defined, and withdrawing the web from the spreading member against the biassing infiu ence of said terminal portion.

By a marginal zone" is meant an area of the web adjoining a longitudinal edge of the web.

The Term hinge is herein employed to indicate any suitable means, for example a ball and socket joint, for enabling a terminal portion of the spreading member to move freely about the longitudinal axis ofthe spreading member.

The present invention is applicable to the conveying and treating of webs of any material. In particular it is concerned with films of thermoplastic materials which may be oriented or unoriented.

Oriented thermoplastic film is commonly produced by a tubular process in which a thermoplastic material is extruded from an annular die orifice in the form of a tube which is subsequently stretched in the longitudinal direction by passage between spaced apart pairs of nip rollers, the second of which pairs rotates more rapidly than the first. Simultaneous stretching of the tubular film in a lateral direction may, if desired, be achieved by inflating the tube with air or gas under pressure. The tubular film may then, if desired, be slit to form a flat film, the slitting being effected before or after heat-setting or other treatments are applied to the film.

Slitting of the tubular film is conveniently achieved by collapsing the tube to a substantially fiat configuration, and introducing one or more longitudinal slits into the tube to produce the required number of planar strips of film. A particularly suitable method of slitting involves the use of two cutting devices, each of which slits only one thickness of film, the slits being effected on opposite sides of the collapsed tube at a point located inwardly of an extreme longitudinal edge thereof, to produce two separate webs. By virtue of the cross sectional shape of the collapsed tube, each of the two webs cut therefrom includes an overturned edge flap which has to be unfolded before the slit web is reeled up. If the overturned flap is unfolded by passing the film over a rigid bar or roller extending transversely of the film, it is observed that the outer-most edge of the unfolded flap. i.e. the edge formed by slitting inwardly of the extreme edge of the collapsed tube, traverses a path of greater length than does the remainder of the film and is thereby placed in a state ofconsiderable tension with the result that the edge of the film becomes stretched and the film neither feeds smoothly during subsequent stages in the processing of the film, nor winds up uniformly on the take-up reel at the end of the process. To avoid these defects it is desirable to ensure that all elements of the film travel over paths of substantially equal lengths from the point at which the edge flap begins to unfold to the point at which the flap is completely unfolded to form a substantially planer film, thereby to equalise the tension across the width of the film. The present invention is particularly suitable for equalising the longitudinal tension in a film while an edge flap of the kind described is unfolded.

According to the present invention we also provide apparatus for equalising the longitudinal tension in a continuous travelling web which apparatus comprises a hinged spreading member to be disposed transversely of the web, means for feeding the web around the spreading member and means for withdrawing the web from the spreading member, wherein the spreading member comprises a body member. a terminal member extending from and hingedly connected to an end of the body member. and means for resiliently biassing at least said terminal member into tensioning engagement with at least a marginal zone of the web.

According to one embodiment of our invention the spreading member comprises a rigid rod or body member disposed transversely of the web and terminating short of a longitudinal edge of the web. A terminal member comprising another rigid rod is hingedly connected to the end of the first rod for pivotal movement against the web. and extends at least as far as, and preferably beyond, the longitudinal edge of the web. Resilient biassing means are provided to urge the terminal member into engagement with a marginal portion of the travelling web, thereby to tension the edge of the web against the forces withdrawing the web from the spreading member.

In operating the apparatus of the present invention a web is passed around the body member so that a suitable contact angle, conveniently of the order of 30 to 180, preferably about 90, is maintained between the web and body member, the terminal member being biassed into the contact angle to tension the web. In a preferred arrangement the terminal member is mounted for pivotal movement in a plane substantially parallel to that along which the web is to be withdrawn from the spreading member.

The relative length of the body and terminal members is not critical. For example, the lengths may be approximately equal, the terminal member being hinged to the body member at a point located approximately midway between the edges of the web. However, particularly for the unfolding of an overturned edge flap, we prefer that the body member should be of a length such as to engage at least 60 percent, and preferably at least percent, of the width of the web. In practice, the relative lengths are selected so as to ensure that the junction between the flap and the remainder of the web contacts the spreading member in the region of the hinge.

In an alternative arrangement which is particularly suitable for unfolding a web both edges of which are folded over in the form of a flap (produced by making a single longitudinal slit in a collapsed tubular web), the spreading member may comprise three components, a centrally located body member to engage and support an innermost section of the travelling web. and a terminal member hingedly connected to each end of the body member to engage respective edge sections of the web.

If desired, the, or each, terminal member may itself be hinged at one or more points intermediate its ends for pivotal movement in the plane of the web, this arrangement being particularly suitable for opening up a web the edge of which has been folded over upon itself more than once.

Conveniently the spreading member comprises rigid bars, particularly cylindrical bars, or rotatable rollers, but it is important that the travelling web does not become wrinkled as it passes around the spreading member, and we, therefore, prefer to employ rigid cylindrical, non-rotatable bars rather than rollers which, when they rotate at an angle to the path traversed by the web, tend to induce wrinkling of the web. Scratching of the web surface can be minimized or prevented by maintaining a thin cushion of gaseous fluid, such as air between the web and the spreading member, and this is conveniently achieved by supplying gaseous fluid under pressure to the interior of some or all of the rods consti tuting the spreading member, and allowing the gaseous fluid to discharge from holes in the surface of these rods. Preferably at least the terminal member which is biassed against the web surface is provided with a gaseous cushion of this kind.

Biassing of the terminal member into engagement with the marginal portion of the web is achieved by any convenient means for example, by a coiled compression spring or by a simple hydraulic or pneumatic system positioned to operate across the hinged joint in the spreading member. Desirably the load/deflection characteristics of the biassing means are selected by simple experimental trial to ensure that the included angle of the hinged joint is such as to reduce the incidence of wrinkling in the web.

To ensure free movement of the terminal member relative to the body member we prefer that the hinged connection therebetween should include a ballor rollerbearing-mounted pivot. lnevitably, a small gap occurs between adjacent members in the hinged joint, and we prefer that this gap should be plugged with a resilient material which, while permitting free movement of the joint, protects the surface of the web against damage. Sponge rubber or foamed thermoplastic material is suitably employed for this purpose, and may, if desired, be covered with a layer of nylon or similar fabric which contacts the web surface.

The rigid rods which constitute the spreading member of the invention are suitably fabricated from mild steel, although we prefer that the surface of each rod be polished to reduce the risk of damaging the web surface. A chromium plated mild steel rod is particularly suitable for this purpose.

As hereinbefore described, the present invention is particularly suitable for use in opening up an overturned edge flap on a travelling web. This is readily achieved by feeding the unfolded web around the spreading member and unfolding the flap by any convenient method for example manually, or by directing a jet of gaseous fluid, such as compressed air, into the interior angle of the flap, i.e. the included angle between the flap and the remainder of the web, so that the unfolded flap runs over and in contact with the terminal portion of the spreading member. Once the flap is unfolded in this way, unfolding continues as a selfperpetuating operation as the folded web approaches and passes over the spreading member. To ensure that the unfolded flap does not fold back again. we prefer that a continuous stream of gaseous fluid, such as compressed air. is directed against the surface of the un' folded fiap which contacts the terminal portion, the stream of gaseous fluid being conveniently emitted from a jet located in the vicinity of the hinged joint of the spreading member.

Desirably. when an edge flap of the kind described is unfolded, the junction between the flap and the remainder of the web should be in contact with the terminal member rather than with the body member, and should remain in the vicinity of the hinged joint to prevent wrinkle formation of the web. Preferably, therefore, the spreading member is slidable transversely of the web to facilitate the positioning of the aforementioned junction outwardly, i.e. on the terminal side, of the hinged joint of the spreading member. Although this slidable adjustment may be effected while a web is passing around the spreading member. we prefer that the adjustment should be made before the web is fed to the spreading member.

In the course of unfolding an edge flap, the terminal member is conveniently displaced about the axis of the hinged joint in the direction of withdrawal of the web at an acute angle, for example of the order of 10 to 30, relative to the longitudinal axis of the body member. This angle is, as hereinafter described. related to the transverse dimension of the edge flap of the folded web. Consequently, the terminal member of the spreading member of the present invention being resiliently biassed against the travelling web, is capable of adopting varying angular positions relative to the body member and is therefore suitable for unfolding flaps of either constant or varying transverse dimensions, that is, the spreading member is suitable for unfolding webs both with a linear and with a non-linear edge profile.

Variation of the transverse edge flap dimensions may arise for a number of reasons. For example, stabilisation of the inflated bubble in the tubular film-forming process is difficult, and the bubble may oscillate randomly about its axis to an extent sufficient to cause variation in the edge profile of the resultant slit film. In particular, the tubular film may be slit by the method disclosed in copending British patent application No. 3267l/7O (corresponding to Dutch application No. 71 09083) which involves slitting the film with a slitting means which oscillates across the direction of travel of the film, and adjusting the position of the film relative to a take-up reel whereby successive layers of film wound onto the reel have their adjacent edges lying in a plane substantially perpendicular to the longitudinal axis of the reel. When this method of slitting is employed the transverse dimensions of the edge flap follow an approximately sinusoidal pattern along the length of the film. The spreading member of the present invention is therefore particularly suitable for use in conjunction with the oscillating slitting system of copending British patent application No. 32671/70.

The present invention is suitable for use in the production or treatment of oriented or unoriented films of thermoplastic materials such as, polymers and copolymers of olefins, such as ethylene, propylene, butene and 4-mcthyl pentene-l, of vinyl chloride, vinylidene chloride, styrene and methyl methacrylate, polyamides such as the various nylons, polysulphones, cellulose and derivatives thereof, and polyesters such as polyethylene terephthalate and polyethylene-l ,2- diphenoxyethane-4,4-dicarboxylate.

The invention is illustrated by reference to the accompanying drawings in which,

FIG. 1 is a simplified schematic representation of a film spreading member in operation,

FIG. 2 is a plan view of the spreading member shown in FIG. 1,

FIG. 3 is a plan view of the hinged joint section of the spreading member shown in FIG. 1,

FIG. 4 is a view along the line l\/IV of FIG. 3, and

FIG. 5 is a simplified plan view of an alternative form of spreading member.

Referring to FIG. 1, a thermoplastic polypropylene film I having an overturned edge flap 2 is shown passing around an idler roller 3, over a spreading member 4 and on to a wind-up roller 5. The width ofthe film in contact with the spreading member was *1 .75 metres, and the width of the edge flap (dimension b) varied between 48 mm and 200 mm, the film having been obtained by slitting a tubular film (diameter L12 metres) using an oscillating slitting technique.

The spreading member 4 includes a rigid, mild steel bar 6 and two shorter bars 7 and 8 of the same diameter 57 mm) as bar 6, the shorter bars being hinged to the ends of bar 6 for pivotal movement in the plane of the film as it is withdrawn towards roller 5.

In setting up the system of the present invention the film is first unfolded by hand and threaded around bar 6. During subsequent operation, when the film is being continuously wound up onto roller 5, unfolding of the overturned edge flap 2 commences as the film passes around roller 3 and is completed as the film leaves bar 8.

To maintain uniform tension across the film it is necessary to ensure that adjacent elements across the width of the film travel over a path of constant length during the unfolding of the flap. This is achieved in the present invention by variation of the angle through which the bar 8 is displaced against the resilient biassing means (not shown) urging the bar into engagement with the marginal zone 9 of the film.

That the angle largely depends on the transverse di mensions of the edge flap 2 can be shown as follows for the case in which a contact angle, a, of 90 is employed:

Consider the system shown in FIG. 1 in which the vertical separation between roller 3 and bar 6 is represented by a", the transverse dimension of flap 2 by b", the horizontal separation between bar 6 and the point at which the film passes over bar 8 as c, the length of the outermost edge 10 of the film distributed between roller 3 and bar 8 as L, and the angle through which bar 8 is displaced relatively to bar 6 as From simple geometrical considerations,

tan 6 c/b.

The condition that adjacent film elements should traverse equal path lengths is,

L a c Now L a c (2b) and L (a C)2. Therefore,

a c 2ac a c (2 and In the present system, the dimension a is constant. Thus, c a b and tan 6 (/19 Kh /b K'b, where K is a constant. Angle H is, therefore, governed by dimension Referring now to FIGS, 2, 3 and 4, the film 1 with the edge flap unfolded to form a marginal portion 9 is shown passing over the spreading system.

Bar 8 is hinged to bar 6 by means of a roller-bearing 11 attached to bar 6 by a bracket 12, and biassing of bar 8 against the marginal portion 9 of the film is achieved by compression spring 13 located between brackets 14 and 15 mounted respectively on bars 6 and 8. It will be appreciated that bar 8 can be pivoted into line with the axis of bar 6, i.e. angle 6 is 0, but in normal operation 0 is usually of the order of 10 to about 30.

A nylon covered sponge pad 16 is located in the gap formed by the hinged joint, to prevent damage to the surface of the film, and air under pressure can be directed from jet 17 into the hinged area to prevent the marginal portion 9 folding back upon the film l. A further supply of air from a suitable source (not shown) can be provided within the spreading member and ejected from orifices 18 to maintain a protective cushion of air between the film and spreading member, thereby preventing scratching of the film surface.

The spreading member shown in FIG. 5 is suitable for maintaining substantially uniform tension in an unfolded film, and comprises two rigid bars 20, 21, hingedly connected as before in end to end relationship, and biassed apart about the hinged joint into engagement with a film 22, which is being continuously withdrawn over the spreading member. A substantially uniform tension is thereby achieved across the width of the film with a consequent reduction in the incidence of wrinkles in the processed film.

I claim:

1. A method of maintaining substantially uniform longitudinal tension in a travelling web which comprises feeding the web around a hinged spreading member disposed transversely of the web, said spreading member comprising a body member and a terminal member extending from and hingedly connected to an end of the body member, resiliently biassing at least said terminal member into cooperating engagement with at least a marginal zone of the web, so that the terminal member is capable of adopting varying angular positions relative to the body member to maintain the desired web tension, and withdrawing the web from the spreading member against the biassing influence of the terminal member.

2. A method of maintaining substantially uniform longitudinal tension in a travelling web having an overturned edge flap comprising unfolding the overturned edge flap, feeding the unfolded web around a hinged spreading member disposed transversely of the web, said spreading member comprising a body member and a terminal member extending from and hingedly connected to an end of the body member, resiliently biassing said terminal member into cooperating engagement with the unfolded edge flap, so that the terminal member is capable of adopting varying angular posi tions relative to the body member to maintain the desired web tension, and withdrawing the unfolded web against the biassing influence of the terminal member.

3. A method according to claim 2 in which the unfolded web is fed around the hinged spreading member so that the junction between the edge flap and the remainder of the web contacts the spreading member in the region of the hinge.

4. A method according to claim 2 in which a thin cushion of gaseous fluid is maintained between the web and the spreading member.

5. A method according to claim 2 in which the junction between the edge flap and the remainder of the web is positioned relative to the hinged region of the spreading member by sliding the spreading member transversely of the web.

6. A method according to claim 2 in which the terminal member is so biassed that all elements of the web travel over paths of substantially equal lengths from the point at which the edge flap begins to unfold to the point at which the flap is completely unfolded.

7. Apparatus for equalizing the longitudinal tension in a continuous travelling web comprising a hinged spreading member to be disposed transversely of the web, means for feeding the web around the spreading member and means for withdrawing the web from the spreading member, wherein the spreading member comprises a body member, a terminal member extending from and hingedly connected to an end of the body member and means for resiliently biassing at least said terminal member into tensioning engagement with at least a marginal zone of the web. said terminal member being capable of adopting varying angular positions rel ative to the body member to maintain the desired web tension.

8. Apparatus according to claim 7 in which the termi nal member is hingedly connected for pivotal movement in a plane substantially parallel to that along which the web is to be withdrawn from the spreading member.

9. Apparatus according to claim 7 in which the spreading member comprises a body member to engage and support an innermost section of the travelling web. and a terminal member hingedly connected to each end of the body member to engage respective edge sections of the web.

10. Apparatus according to claim 7 in which the surface of the terminal member is perforated to allow gaseous fluid to discharge from the interior of the body member.

11. Apparatus according to claim 7 in which a resil ient plug is provided in the hinged joint between the body member and terminal member.

12. Apparatus according to claim 7 in which a jet is provided to deliver a continuous stream of gaseous fluid against the surface of the unfolded web which contacts the terminal member.

13. Apparatus according to claim 7 in which the spreading member is slidable transversely of the web. =l

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,907,186 DATED September 23, 1975 INVENTOR(S) Robin Hasler It is certified that error appears in the ab0veidentified patent and that said Letters Patent are hereby corrected as shown below:

At paragraph [76] on the front page format, after "Robin Hasler," delete "52 Camper Crescent," and insert ---52 Cowper Crescent,--

After paragraph [76] insert: --[73] Assignee: Imperial Chemical Industries Limited, London, England-- Signed and Scaled this twenty-fourth Day Of February 1976 [SEAL] A nest:

RUTH C. MASON C. MARSHALL DANN Alresling Officer (mnmissrmu'r uj'ParenIs and Trademarks 

1. A method of maintaining substantially uniform longitudinal tension in a travelling web which comprises feeding the web around a hinged spreading member disposed transversely of the web, said spreading member comprising a body member and a terminal member extending from and hingedly connected to an end of the body member, resiliently biassing at least said terminal member into cooperating engagement with at least a marginal zone of the web, so that the terminal member is capable of adopting varying angular positions relative to the body member to maintain the desired web tension, and withdrawing the web from the spreading member against the biassing influence of the terminal member.
 2. A method of maintaining substantially uniform longitudinal tension in a travelling web having an overturned edge flap comprising unfolding the overturned edge flap, feeding the unfolded web around a hinged spreading member disposed transversely of the web, said spreading member comprising a body member and a terminal member extending from and hingedly connected to an end of the body member, resiliently biassing said terminal member into cooperating engagement with the unfolded edge flap, so that the terminal member is capable of adopting varying angular positions relative to the body member to maintain the desired web tension, and withdrawing the unfolded web against the biassing influence of the terminal member.
 3. A method according to claim 2 in which the unfolded web is fed around the hinged spreading member so that the junction between the edge flap and the remainder of the web contacts the spreading member in the region of the hinge.
 4. A method according to claim 2 in which a thin cushion of gaseous fluid is maintained between the web and the spreading member.
 5. A method according to claim 2 in which the junction between the edge flap and the remainder of the web is positioned relative to the hinged region of the spreading member by sliding the spreading member transversely of the web.
 6. A method according to claim 2 in which the terminal member is so biassed that all elements of the web travel over paths of substantially equal lengths from the point at which the edge flap begins to unfold to the point at which the flap is completely unfolded.
 7. Apparatus for equalizing the longitudinal tension in a continuous travelling web comprising a hinged spreading member to be disposed transversely of the web, means for feeding the web around the spreading member and means for withdrawing the web from the spreading member, wherein the spreading member comprises a body member, a terminal member extending from and hingedly connected to an end of the body member and means for resiliently biassing at least said terminal member into tensioning engagement with at least a marginal zone of the web, said terminal member being capable of adopting varying angular positions relative to the body member to maintain the desired web tension.
 8. Apparatus according to claim 7 in which the terminal member is hingedly connected for pivotal movement in a plane substantially parallel to that along which the web is to be withdrawn from the spreading member.
 9. Apparatus according to claim 7 in which the spreading member comprises a body member to engage and support an innermost section of the travelling web, and a terminal member hingedly connected to each end of the body member to engage respective edge sections of the web.
 10. Apparatus according to claim 7 in which the surface of the terminal member is perforated to allow gaseous fluid to discharge from the interior of the body member.
 11. Apparatus according to claim 7 in whiCh a resilient plug is provided in the hinged joint between the body member and terminal member.
 12. Apparatus according to claim 7 in which a jet is provided to deliver a continuous stream of gaseous fluid against the surface of the unfolded web which contacts the terminal member.
 13. Apparatus according to claim 7 in which the spreading member is slidable transversely of the web. 